This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Bren group from the University of Rochester's Department of Chemistry utilized the X-Band EPR instrumentation at ACERT to study a series of bacterial cytochrome c (cyt c) variants. These studies were part of an on-going investigation of the functional implications of out-of-plane distortions of the heme cofactor. The continuous-flow, liquid helium cryostat available at ACERT is essential for these experiments because the EPR spectra of cyts c are typically not observed above 30 K due to a relatively short spin-lattice relaxation time.